I've seen leakdown testers for under $100 so it's not that much of an investment if you already have an air compressor.
I think leakdown tests are done at 100psi or so. Nowhere near the 150-180psi a healthy gasoline engine imposes on itself or the 400psi or so a healthy Diesel engine imposes on itself.
My amateur opinion is that you perform a compression test to get a general feel for the engine. If compression checks out (all cylinders are strong and little variation among cylinders) then there's little reason to do a leakdown test. If compression is below spec or on the low side of spec on any cylinder, a leakdown test will help you figure out what's going on (rings, valves, head gasket).
I don't know if a formal leakdown test tells you more than an informal leakdown test in which you pump air into the cylinder and use your eyes and ears to figure out where it's leaking. AFAIK
, a formal leakdown test adds only a number such as 5% leakdown. I don't know what to do with that number. No suggestions, please